1. Field of the Invention
The present invention relates to apparatus for stacking sheets, and in particular, sheets issuing from a copier or printer.
2. Description of Related Art
In many automatic copying machines, the geometry of the machine elements is such that with the paper path the copies produced have the image on the top side. Thus sequential copies enter the collecting tray with the copy or image side up. This is satisfactory if only a single copy of a single image is desired or if multiple copies of a single image is desired. In both cases, no distinction between sequential copies is required and all copies may be readily collected with the image side up. It is also satisfactory if the original documents fed to the copying machine are fed in reverse order, last or bottom sheet first and first or top sheet last. In this instance the collected set has the top sheet face up on top and the bottom sheet face up on the bottom of the set. However, in most instances of copying set of documents, the set is face up with top sheet on the top and if copied according to normal procedures, the top sheet number one is copied, producing a copy face up and a set so produced has sheet number one face up on the bottom and the last sheet face up on the top. It can therefore be seen that it is desired to obtain the copies in the same order as the original set so that in the set produced by the copying machine the last sheet is on the bottom of the set and the top sheet is on the top of the set, both being face up. In addition, in electronic printing it is also advantageous to be able to print from the first page to the last page in order since if you print from the last sheet to the first sheet the substance of the first to last pages must be stored in the printer's memory thereby increasing the size and cost of the memory required.
This result may be accomplished in copying a set of sheets if the top sheet, number one sheet, is fed first to be copied and the copy produced which is image side up is inverted such that the image is on the bottom side. With copying of successive sheets of a set and inverting each copy the final set is collected face down with the top sheet on the bottom and the bottom sheet on the top.
It is also desirable to provide a system which is capable of inverting and stacking sheets which are supplied at a high speed and/or have a variety of different sizes and weights. Such a system should be capable of registering sheets in a stack so that the front and side edges of each sheet are precisely aligned. A sheet stacking apparatus should also have the ability to offset sets of documents, so as to distinguish individual sets from one another, while maintaining a high degree of alignment of the sheets within each set.
U.S. Pat. No. 3,968,960 to Fedor et al discloses a sheet inverting and stacking apparatus. The apparatus comprises a conveying means, a rotating means for deflecting the leading edge of a sheet from the conveyor means to a stacking platform, a control means for altering the movement of the deflecting means in accordance with the length of the sheet, and a second conveying means above the deflector for moving the trailing portion of the sheet beyond the leading edge to aid in inverting the sheet onto the stacking platform. An overhead assist belt is provided which travels at the main paper path speed for assisting in flipping sheets. The rotation of the disk can be paused for longer sheets. Continuously rotating rolls having a friction surface on their periphery are used to urge the leading edges of deposited sheets onto the stack.
U.S. Pat. No. 4,431,178 to Kokubo et al discloses a bank note accumulator assembly for receiving bank notes. The assembly includes a plurality of paddle wheels, a conveyor, and a guide belt assembly which restrains the free movement of the trailing ends of paper sheets from slipping out of the paddle wheels. The guide belt is disposed at an angle to a carrier plate and moves at a speed substantially the same as the circumferential speed of the trailing free ends of the paddlewheels. A scraper plate is disposed below the paddlewheels for scraping the bank notes from the paddlewheels and into the carrier plate.
U.S. Pat. No. 4,575,069 to Burkhart discloses a sheet feeding mechanism comprising a pivoting deflector arm which deflects the leading edge of a sheet to a front portion of a receiving tray and then forms a buckle in the sheet, the deflector arm moving to a remote location after buckle formation, and a plurality of sheet feeding belts which frictionally feed the remaining portion of the sheet, allowing it to fall to the tray. See FIGS. 2-6. When inversion is not desired, the deflector arm is rotated to the remote position.
U.S. Pat. No. 3,162,439 to Poland et al discloses a document stacking device which includes a pair of slotted, rotating disks which receive, invert and stack documents. A series of rollers located above the disks assist in feeding a document into the disks as the disks rotate from an initial input position.
U.S. Pat. No. 4,436,301 to Doery et al discloses an overhead transport for transporting a document to a position above a document stacking tray in a recirculating document handler.
A variety of other disk stacking devices have been proposed. U.S. Pat. No. 4,712,785 to Stemmle shows a disk stacker including an upstream deflector gate for selectively deflecting documents into the disk for inversion or through a bypass for stacking on the same tray without inversion. Xerox Disclosure Journal Vol. 12, No. 3 (May/June 1987) to Stemmle shows the same arrangement described above. U.S. Pat. No. 3,904,192 to Pfeifer et al shows a disk stacker located at the output slot of a copying machine. JA 63-123754 to Asano shows a stacker for inverting and stacking bills. JA 62-153051 to Uchiumi shows a sheet stacking device which employs a conveying belt to ensure complete entry of a sheet to be stacked into the blades of an impeller. European Patent Application EP 59,101 A1 to Ariga et al and European Patent Specification EP 121,499 B1 to Nakamura disclose devices for stacking sheets wherein a predetermined number of notes are accumulated and stacked.
U.S. Pat. No. 4,385,756 as well as U.K. Patent Application No. GB 2,082,550A, both to Beery, disclose a disk stacker which includes a fixed sheet guide which assists in guiding sheets into the disk slots.
U.S. Pat. No. 4,088,314 to Phillips discloses a synchronous stacking device having a rotatable carrier with pockets. FIG. 2 shows a stacking device including a carrier comprising slotted disks. A guide track comprising wires is provided and is capable of being moved by a solenoid from a normal position to a deflecting position for deflecting a document which is not aligned with a slot.
U.S. Pat. No. 4,252,309 to Garrison et al discloses a spring-biased clamping member which secures a sheet within the slotted grooves of an inverting wheel during a sheet-inverting rotation. An edge clamp toggles along pins between two positions to secure the leading edge of a copy sheet within tapered slots of a rotating flipper roller. An angled flat spring presses against a cam surface to cause the clamp to engage (position B) and then disengage (position C) to hold and then release a sheet during a stacking process.
U.S. Pat. No. 4,600,186 to von Hein et al discloses a mechanism for reducing the impact speed of printing products as they enter into the pockets of a rotary delivery flywheel. The speed reduction mechanism includes a cam plate mounted adjacent the periphery of a rotary sheet delivery flywheel. The cam plate rotates in a direction opposite to the flywheel. Cams mounted on the cam plate rotate into closely spaced relation to rotatable fixed support rings to catch a trail edge of a printing product as it is being fed into a slot of the flywheel.
U.K. Patent No. 1,464,132 to Brooke discloses an engaging mechanism which grips the leading edge of an envelope as a drum rotates through a series of electrostatic reproduction stations.
U.S. Pat. No. 4,431,177 to Beery et al discloses a disk stacker which includes a pivotally mounted arm which moves an offset registration member in a direction to selectively offset sheets in the rotating disk.
U.S. Pat. No. 4,568,172 to Acquaviva discloses a copier which outputs a stack of sheets wherein individual sets in the stack are offset in the process direction.
A number of devices for tamping one or more edges of a sheet stack to improve the registration thereof are known. Examples of tamping devices include those disclosed in U.S. Pat. Nos. 4,318,541; 4,147,342; 3,933,352; 3,733,070; 3,982,751; 4,556,211; and 4,844,440.
U.S. Pat. No. 3,847,388 to Lynch discloses a device for stacking sheets of cut material in alignment within a collecting tray. An extended flapper element of elastomeric resilient material is coaxially aligned with one of a pair of cooperating pinch rollers arranged to deliver sheets into a collecting tray. The flapper is deformed into a load condition as it is drawn into the nip formed between the cooperating rolls and, upon passing through the nip, is released against the uppermost sheet delivered into the tray imparting energy stored therein to the sheet effecting alignment of the sheet within the tray.
U.S. Pat. No. 4,228,997 to Schoonmaker et al discloses a stacking machine for stacking random sized sheets. The sheets are received by pockets formed by adjacent flexible webs, each web being secured at one end to a disk.
U.S. Pat. No. 4,916,493 to DeVito discloses an exit roller reversal gate for a duplex printer. The gate consists of fingers which are mounted on a pivotal shaft closely adjacent to rollers. The fingers are spring loaded into an up position out of normal sheet engagement. Upon reversing of the rollers, the fingers are moved to a lower position substantially extended outside the radius of the roller to push away and hold sheets already in an exit tray from being engaged in rollers.
The disclosed apparatus may be readily operated and controlled in a conventional manner with conventional control systems. Some additional examples of control systems for various prior art copiers with document handlers, including sheet detecting switches, sensors, etc., are disclosed in U.S. Pat. Nos.: 4,054,380; 4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401; 4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344; 4,284,270, and 4,475,156. It is well know in general and preferable to program and execute such control functions and logic with conventional software instructions for conventional microprocessors. This is taught by the above and other patents and various commercial copiers. Such software will of course vary depending on the particular function and the particular software system and the particular microprocessor or microcomputer system being utilized, but will be available to or readily programmable by those skilled in the applicable arts without undue experimentation from either verbal functional descriptions, such as those provided herein, or prior knowledge of those functions which are conventional, together with general knowledge in the software and computer arts. Controls may alternatively be provided utilizing various other known or suitable hardwired logic or switching systems.
All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features, and/or technical background.